Project Summary Asthma is the most common chronic disease among children and the leading cause of emergency care and hospitalization in children. Even though multiple asthma therapies exist, the high rate of incomplete efficacy in asthma treatment (40%-70%) highlights the need for alternative individualized therapies based on a better un- derstanding of disease mechanisms. To date, the molecular mechanisms underlying the etiology and patho- genesis of childhood asthma are not fully understood. This proposal directly fills in this gap in knowledge and tests a novel hypothesis addressing disease mechanism. Methylcytosine dioxygenase TET1 modifies 5?- methyl-cytosine and regulate gene function. In addition to its catalytic activity, TET1 protein recruits histone modifying protein complexes through interaction with transcription factors (TFs) to regulate histone marks and chromatin accessibility, leading to both activation and repression of gene expression. We were the first to show that in airway epithelial cells, higher TET1 promoter methylation is associated with lower TET1 expression and more frequent asthma symptoms in children. Further, we found that overexpression of TET1 in HBECs (human bronchial epithelial cells) leads to transcriptional downregulation of interferon (IFN) signaling pathway. Consist- ently, loss of TET1 in HBECs significantly increases the expression of IRF7 and its downstream target type I IFN following HDM challenges. Finally, loss of Tet1 causes increased lung expression of IFN signaling path- way and leads to enhanced airway hyperresponsiveness and lung inflammation in mouse models of asthma. Collectively, these data support an overall protective role of TET1 in asthma severity through inhibition of type I IFN signaling. Our data strongly implicate a protein/protein interaction network including IRF7/STAT1/STAT2 in mediating the effects of TET1 on type I IFN induction. Preliminary analysis supports the regulation of IRF7 ex- pression by TET1 through DNA methylation and histone modification. It is well established that airway epitheli- al type I IFN signaling pathway regulates innate and adaptive immune responses to external stimuli and con- tributes to asthma development and exacerbation. Collectively, we hypothesize that Tet1 regulates asthma phenotypes by inhibiting type I interferon signaling through DNA methylation and histone modifications in air- way epithelial cells. Our long-term goal is to understand the epigenetic regulation of childhood asthma. The objective of this R01 application is to identify the mechanism(s) by which TET1 contributes to asthma. This ap- plication will have significant public health impact. Through the proposed aims, we will 1) demonstrate that the transcriptional regulation of type I IFN signaling pathway by TET1 in airway epithelium modulates asthma phe- notypes; 2) define the mechanism(s) by which TET1 regulates type I IFN signaling pathway in normal and asthmatic epithelium; 3) show that Tet1 regulates respiratory virus-induced asthma exacerbation; and 4) pro- vide novel therapeutic targets for asthma and other diseases in which type I IFN signaling pathway is an es- sential player.